Spark plug



Dec. 31, 1935. B o LEMOWE 2,025,994

SPARK PLUG Filed May 21, 1934 INVENTOR,

Bruce aLemoine Patented Dec. 31, 1935 UNITED STATES ATENT FFIQE SPARK PLUG Application May 21, 1934, Serial No. 726,704

1 Claim.

This invention relates, in general terms, to internal combustion engine equipment, dealing particularly with spark plugs employed to electrically fire or explode the gas while under compression in the cylinders.

The ordinary gas engine spark plug has two electrodes or terminals, the electric current passing off one and jumping to the other, for which reason this method of exploding the gas is usually called the jump-spark system, in con trast to the make-and-break method in which the electrodes actually contact and then separate, creating the spark which accomplishes the ignition of the gas.

In the jump-spark system one of the electrodes, or points as they are called in shop parlance, is grounded on the cylinder of the engine through the body of the spark plug and the other is insulated from the plug and in direct connection with the source of electric current generation.

While, in operating a jump spark system, the points are always separated, the extent of this separation has a vital bearing on, and is quite consequential with respect to, attaining the highest efiiciency of the ignition system.

For instance, when an internal combustion engine is being started it is preferable to have the points somewhat closely positioned, relatively, as this tends to make the cold engine start more easily, the revolutions of the crank being at the lowest point and the spark more or less continued; but as the engine increases its speed of rotation and becomes hot, the points work best when the separation of the points, or the spark-gap, is increased, resulting as has been demonstrated in greater efiiciency and economy of operation of the engine.

In the present invention the object I have sought is to provide means whereby the sparkgap may be automatically increased in length as the engine operation proceeds from the start to its normal running condition.

To accomplish this object I incorporate in the spark-plug a third electrode which, from the character of the material and its peculiar shape, changes its form and position, relative to the other electrodes, functioning only at the preliminary stages of the engine operation and thereafter serving no purpose.

The character of the invention may best be understood by reference to the description found in the following specification when taken in connection with the accompanying drawing disclosing an embodiment which, at the present time, I consider preferable to other possible forms in which the invention might be carried out.

In the drawing,-

Fig. 1 is an elevation of a spark plug, partly in section, showing my construction;

Fig. 2 is a view of the lower end of the spark plug showing the disposition of the electrodes at the start of engine operation, and

Fig. 3 is the same as Fig. 2 except that the electrodes are shown in the positions they assume after the engine is running normally.

Similar reference oharactersindicate like parts in all views of the drawing.

Referring to the drawing, l is a spark plug which may be of any conventional design, showing the threaded portion 2 by which the spark plug is secured in the cylinder head of the engine (not shown), and the threaded post 3 to which the wiring connection is made. 2

On the part 4, which extends into the firing chamber of the engine, are the grounded and insulated electrodes or firing points 5 and 6, respectively, these being of the usual construction and common to spark plugs in general.

Inserted and fixed in a slot 4a in the wall of the spark plug is a comparatively thin strip of metal 1, preferably made of an alloy of which tungsten forms a part.

This element 1 is the third electrode in my combination and is made arcuate in shape, with an end abruptly bent toward the central or insulated electrode 6. The strip 1 is rolled in such a manner as to make one side somewhat more closely set than the other side, causing it when heated to change its. form, in this case to straighten.

When assembled on the plug end the electrode 7 assumes the shape and position, relative to the other electrodes, as shown in Fig. 2, the sparkgap being represented by the letter X. In this position the spark will jump the gap between electrodes 6 and l for the reason that at this time the spark-gap is the shorter, or less than the gap Y between electrodes 5 and 6, this latter sparkgap being substantially constant at all times.

When the engine is being started the electrodes are located as they appear in Fig. 2, but upon gaining speed and becoming heated to normal temperature, the electrode "i will changeits form, as shown in Fig. 3.

In the Fig. 3 illustration the electrode 1 has expanded and changed its shape, making the 55 spark-gap Z greater than the fixed or constant spark-gap Y. Consequently, the firing of the gas will now be done by the points 5 and 6, the electrode 1 being for the time functionless.

The spark-gap Y gives a long, intense spark and in practice makes the operation of the motor vehicle more economical, due to the more nearly complete combustion of the fuel, and incidentally more powerful on account of the fact that the fuel in each charge is fully taken advantage of.

But the wide spark-gap Y is not conducive to easy starting, hence the necessity of providing one for the latter purpose, which I doby supplying the expansible electrode 1.

Thus in my spark-plug I have advantages both in starting and in continuous running of the motor, each working in harmony with the other and functioning automatically at the proper times.

For obvious reasons it is believed that my improved spark-plug will, on its merits alone, commend itself and appeal to those who operate motor vehicles.

What I claim is:

A spark plug for an internal combustion engine comprising a body portion adapted to be secured in said engine, an electrode fixed on and grounded through said body portion, an electrode passing through and insulated from said body portion, said electrodes being so disposed, relatively, that a comparatively wide and constantly maintained spark-gap therebetween is provided, and a flat, uni-metal expansible electrode secured in said body portion and having a generally arcuate shape with its free end abruptly turned toward said insulated electrode and so positioned, normally, in relation thereto that a spark-gap of less width than said first mentioned sparkgap is procured, said uni-metal electrode being characterized by possessing a denser granular structure on its concave than on its convex side, whereby upon being heated, incident to operating said engine, a flexing thereof takes place, forming a spark-gap of greater width than said first mentioned spark-gap.

, BRUCE O. LEMOINE. 

